Tight control over redundancy is a new design driver that has emerged for the next generation of 21 cm observatories such as HIRAX[1]}. We are aiming to solve the problem of redundancy in hardware, which requires a level of precision that is significantly higher than existing experiments such as CHIME[2]} and HERA[3]}.
That is, rather than correcting for the differences between array element structures and positions completely in software, we aim to reduce the element differences as much as possible in hardware, before applying fine corrections in software.
This requires significantly more stringent specifications than normal for a radio telescope, on the order of 1 part in 1000 relative to the wavelength, driven largely by the high foreground to signal ratio for the 21 cm signal. Edge effects due to the finite size of the array are also a source of non-redundancy, and must be taken into consideration. Additionally, we are also concerned with minimizing crosstalk between the elements in the array, which can result from either sky signals bouncing between elements, or from amplifier noise being transmitted from one element and picked up in another. The issues we want to address in this work are, broadly, how to optimize the design of the instrument to minimize systematics, and to determine what level of element redundancy is necessary, and whether this level is feasible to achieve in hardware, within cost.
